1. Field of the Invention
The present invention relates to an improved method and apparatus for producing, packaging and deploying beneficial symbiotic mycorrhizal fungi and actinomycete bacteria in association with a source of phosphorus in order to fertilize crops or other plants. The present invention thus relates to a system of plant fertilization utilizing microorganisms for extracting phosphorus from rock phosphate, soil, or commercially refined phosphate sources and distributing these materials to plant root systems without adsorptive loss to clay minerals and other soil constituents.
2. Related Applications
The present application is a continuation-in-part of my copending applications Ser. No. 294,681 filed Aug. 20, 1981, entitled "Microbiological System For Phosphate Extraction and Distribution to Plant Root Systems," and Ser. No. 294,682 filed Aug. 20, 1981, entitled "Preparation of Microorganisms For Use in Soil Innoculation," which are incorporated herein by reference.
3. The Prior Art
It is well known that plants grown in soils which are deficient in soluble phosphorus benefit from association with mycorrhizal fungi (hereinafter referred to as MF) and that similar associations are also formed by actinomycete bacteria (hereinafter referred to as AB). The fungal associations are formed by microorganisms belonging to the family Endogonaceae which constitute two morphological groups: (1) Ectomycorrhizae form principally on the roots of woody plants which include economically important families of forest trees. (2) Endomycorrhizae, also commonly known as vesicular-arbuscular mycorrhizae (hereinafter referred to as VAM), colonize the roots of most food crop plants. Both the endomycorrhizal and ectomycorrhizal fungi develop symbiotic associations with roots of the plant root system, receiving carbohydrates and other nourishment from the plant while directly benefiting the plant by transferring to it phosphorus, water, and other constituents from the soil through a hyphal network.
The uptake of phosphorus by MF can occur in soils deficient in soluble phosphorus due to a low threshold for phosphorus retrieval. Furthermore, the ability of the fungus to form an extensive hyphal network in the soil surrounding the plant root permits phosphorus recovery from a large volume of soil since there may be up to 80 cm of hyphae for each cm of root infected by vesicular-arbuscular endomycorrhizal fungi and an even greater mass for ectomycorrhizal fungi. Individual hyphae project up to 10 cm from the root system of the host plant, thereby penetrating the zone of depletion adjacent to the root cortex and greatly extending the effective volume of soil from which phosphorus, water and other constituents can be extracted.
Phosphorus transfer from the soil to the plant is accomplished within MF by a process termed translocation. MF first concentrate the extracted phosphorus in polyphosphate granules within the cell cytoplasm and then move the granules from soil and inter-root hyphae through the external hyphal net and finally into the plant root through an internal hyphal net. In the case of endomycorrhizal fungi, phosphorous exchange and entry into the plant is believed to occur in part by means of specialized terminal structures or arbuscles, which arise from the internal net and invaginate cells of the root cortex.
Although the use of MF to encourage plant growth has been shown to be feasible and desirable, they have not been employed on a widespread commercialized basis since methods have not been perfected to produce and package MF propagules on a large scale.
An apparent limitation to the production of VAM fungi used in prior applications is the inability to induce these microorganisms to grow and reproduce by means of pure in vitro cultures commonly employed to propagate fungi on a commercial scale. The lack of a technique for producing an effective VAM inoculum by means of a culture technique devoid of plant cells presents an extremely difficult, if not an impossible, challenge to production on a large scale.
Thus, what is needed is a practical means by which MF and AB can be used for encourgaging plant growth in commercial applications. This would require a method for mass producing efficient species of MF and AB in sufficient quantities for large-scale distribution. This would also require that the microorganisms remain viable during storage, transport and implantation into the soil. In addition, the microorganisms would also have to efficiently colonize the roots of host plants so that the latter may benefit from the transfer of phosphorus and other soil constituents.
It is also well known that phosphorus must be in a water soluble form in order to be utilized by plants. Most soils are deficient in such soluble forms of phosphorus despite the fact that some may have moderate to high levels of insoluble or unavailable phosphorus in the form of natural minerals, organic phosphorus compounds, and clay minerals containing adsorbed phosphorus.
In order to satisfy the continuing agricultural need for soluble phosphorus, chemical refinement processes have been utilized commercially to obtain soluble phosphorus from rock, mineral and other phosphates which are soluble in acid. Such chemical processes are not only complex and energy-intensive, but they generally require "high-grade" rock phosphate, the natural United States sources of which are becoming depleted.
It is common practice to apply a refined phosphorus fertilizer directly to the soil prior to the growing season in order to provide a source of soluble phosphorus; however, no means has been provided for preventing loss of this soluble phosphorus while in the soil through adsorption by clay minerals. A high proportion, often in excess of sixty percent (60%), of the soluble phosphorus applied as fertilizer to argillaceous soils may be lost due to adsorption of phosphorus by clay and iron minerals, or by incorporation into organic compounds which are normal soil constituents. The phosphorus adsorbed by the clay minerals becomes irreversibly bound leading to permanent loss of much of the phosphorus fertilizer applied to the soil.
A further problem with direct application of soluble phosphorus fertilizers to the rhizosphere of the plant root system is a condition referred to as phosphorus toxicity. This condition occurs when the phosphorus within a plant exceeds optimal levels for growth, and it may result in stunting. Thus, the application of fertilizer granules of soluble phosphorus may produce an initially high level of phosphorus in the soil and may result in decreased growth in the nearby plants.
In seeking to overcome these problems, attempts have previously been made to utilize unrefined rock-phosphates or microorganisms or combinations thereof in a soil environment near plant root systems in order to provide soluble phosphorus to those root systems. These attempts have been based on the understanding that soluble phosphorus compounds may be derived from natural minerals and organic phosphorus compounds through the action of bacterial microorganisms, as well as by organic and inorganic acids. Such attempts are reflected in the disclosures of U.S. Pat. Ser. Nos. 947,795, 1,361,597, and 4,155,737. However, these attempts have not succeeded in providing a stable microenvironment necessary for sustaining growth of the bacterial microorganisms capable of converting insoluble into soluble phosphorus compounds.
In the past, attempts to produce soluble phosphate from existing insoluble sources within the soil have generally been unworkable. Most soils in temperate climates do not provided the conditions of low pH which are conducive to the spontaneous conversion of insoluble forms of phosphorus to soluble forms of phosphorus. Insolubility may thus be related in part to a neutral or alkaline soil pH and to a lack of other inorganic and organic factors in the soil which would favor the conversion of insoluble to soluble forms of phosphorus. The problem of providing a substantial mineral or other unrefined source of soluble phosphate for plant fertilization in most types of soils has not been suitably solved by the prior art.
Laboratory and limited field experiments have utilized MF microorganisms for securing and transferring naturally occurring phosphorus from the soil to adjacent plant root systems. In vitro laboratory tests and recent field experiments have also demonstrated that certain MF are capable of translocating soluble phosphorus from a plant with high levels of phosphorus to a plant which is deficient in phosphorus. However, high levels of soluble phosphorus may reduce the incidence of MF associated with the plant roots, and none of the above-described methods and devices provide a full and workable organic approach to the problem of supplying soluble phosphorus to plants either in sufficient quantity or without loss through adsorption.
What is needed to fully overcome the deficiencies of the prior art is a means for the controlled mobilization of soluble phosphorus from one or more sources and its transfer to plant root systems without appreciable loss to clay minerals and other adsorptive constituents within the surrounding soil. It would be a further important improvement to provide a means for supplying phosphorus to plant systems from unrefined sources of rock phosphate. Another desirable improvement would be to provide a phosphorus supply which would be available over an extended period of time, such that the plant nutrient requirements are met without phosphorus toxicity. A still further advance in the art would be to provide a means for balancing the phosphorus levels so as to transfer phosphorus from plants which have an adequate or relatively high level of phosphorus to those deficient in phosphorus.